Japanese Laid-Open Patent Publication No. 3-249686 discloses an example of producing one-step Lippman type hologram which has vertical and horizontal parallax.
FIG. 6 is a drawing showing the configuration of an apparatus for producing two-dimensional hologram disclosed in the above Publication. In this apparatus for producing the hologram, the laser light, which is output from a laser light source 103, is branched into two beams by a beam splitter 104. One of the branched laser light is expanded in diameter of luminous flux, and enters a spatial optical modulating element F′ such as transmissive liquid crystal display device and so forth. After being subjected to an amplitude modulation at each pixel of the spatial optical modulating element F′, which displays images viewed from each observing point created by a computer, the beam interferes with a reference light, which enters a photosensitive material 111 from the backside thereof by means of a lens, so that the element hologram is formed on the photosensitive material 111.
Thus, dot-like element holograms are arranged in a matrix-like configuration at 0.3–0.5 mm intervals on the photosensitive material 111, and thus, the Lippman type holograms are made out. And, when reproducing the image, by irradiating the holograms with a parallel pencil having a large luminous flux diameter from the same direction as the incident direction of the above reference light, reproduced waves are generated from each element hologram on the holograms 111; thus an object image is reproduced.
However, since the number of the element holograms, which are recorded by one recording, is limited to one, there is such problem that it takes an extremely long recording time for recording all element holograms. Conventional examples for solving the problem are described below.
(Conventional example 1) Japanese Laid-Open Patent Publication No. 2001-183962 discloses a method for producing hologram, in which a plurality of element holograms are recorded at one time while eliminating reducing optical system. In the method for producing hologram set forth in the above Publication, 3×4 images having different observing point are displayed on a liquid crystal panel, and the laser light, which have passed through the liquid crystal panel, is subjected to a modulation. The laser light, which contains image information of the liquid crystal panel, passes through a lens array composed of 3×4 convex lenses. By disposing a mask, which determines the size of the element holograms, and a photosensitive material in a rear-side focal plane of the convex lens array, twelve element holograms having the same intervals as that of the display images and the size same as the opening of the mask can be recorded at one time. In this method, in order to record the element holograms on the entire surface of the photosensitive material, the exposure is carried out while shifting the photosensitive material by a distance equivalent to the size of the mask opening.
(Conventional example 2) “M. Yamaguchi, H. Endoh, T. Koyama, N. Ohyama, “High-speed recording of full-parallax holographic stereograms by a parallel exposure system” (Opt. Eng. 35(6) 1556–1559 (June 1996))” discloses a method for producing holograms in which twelve element holograms are recorded at one time. According to this document, 3×4 images with a different observing point respectively are displayed on the liquid crystal panel, and the laser light, which has passed through the liquid crystal panel, is subjected to modulation. The laser light, which contains image information of the liquid crystal panel, passes trough a lens array, which is constituted of 3×4 concave lenses. The light, which has passed through the respective concave lenses, are reduced by an a focal reducing optical system, which is composed of a combination of two convex lenses, and projected onto a photosensitive material. Here, the front-side focal position of the concave lens and the surface of the photosensitive material constitute an image forming relationship in the reducing optical system. According to this method for producing holograms, in order to record the images on the entire surface of the photosensitive material, the exposure is carried out while shifting the photosensitive material by a distance equivalent to three or four times of the element holograms.